Degradation and stress response mechanism of Cryptococcus podzolicus Y3 on ochratoxin A at the transcriptional level

Effects of human immunoglobulin A on Cryptococcus neoformans morphology and gene expression

Human IgM was previously shown to inhibit Titan-like cell formation of Cryptococcus neoformans, whereas IgG did not. Here, we conducted an in-depth analysis of the effect of normal human IgA on C. neoformans biology (strain H99) and compared it to that of IgG and IgM. We found that like IgM, IgA affected H99 cell size and morphology. The total size of cells cultured with IgA was significantly smaller at 24 h than cells cultured with IgM and IgG and comparable to IgM but smaller than IgG at 72 h. We also examined extracellular vesicle (EV) production and found that it was significantly reduced in cells cultured with IgA than the control, but the EVs were larger. To further probe the effect of IgA on H99, we performed expression profiling by RNAseq of H99 cells cultured with each immunoglobulin isotype and compared the results with IgA to those with IgM, IgG, and a control (PBS). These comparisons showed that cells cultured with IgA overexpressed genes related to cell rescue, defense, virulence, energy conservation, adapation to stress with CNAG_00735 (aldehyde dehydrogenase family seven member A1) being the most overexpressed, and repressed some genes related to vesicular transport, including CNAG_04306 (vesicle transporter SFT2B) and CNG_00063 (histone H3). Collectively, our findings suggest that the effects of IgA on cryptococcal biology deserve further investigation, as they reveal new insights into human host-C. neoformans interaction, which suggest that antibody responses may affect gene expression in C. neoformans.IMPORTANCEProfound CD4 T cell deficiency is associated with the development of cryptococcosis in HIV-infected individuals. However, perturbations in antibody immunity, including reduced levels of plasma IgA and IgM, have also been associated with cryptococcal disease status. While IgM has been studied in some detail, IgA has not. Here, we evaluated the effect of normal human IgA on Cryptococcus neoformans biology and morphology to expand knowledge of the role that it may play in cryptococcal pathogenesis.

Analysis of Microbial Diversity Dominating Nitrite Enzymatic Degradation and Acidic Degradation in the Fermentation Broth of Northeast Sauerkraut

Nitrite hazard is an important food safety issue in the production process of Chinese Northeastern sauerkraut, but this nitrite can be eliminated through microbial enzymatic degradation and acidic degradation as fermentation progresses. Therefore, analyzing the microbial diversity that dominates nitrite degradation in Chinese Northeastern sauerkraut can provide a reference for its safe production. In this study, based on the dynamic monitoring of nitrite concentration, pH, and the abundance of nitrite reductase genes (nirK and nirS) and the application of high-throughput sequencing technology and various statistical analysis methods, the microbial groups associated with nitrite enzymatic degradation and acidic degradation in Northeast sauerkraut fermentation broth were analyzed. During the nitrite peak period of Northeast sauerkraut fermentation broth, the nitrite concentration reached 32.15 mg/kg, the pH was 4.7, and the abundances of the nitrite reductase genes nirK and nirS were 3.0 × 104 and 4.9 × 104 copies/μL, respectively. At this stage, nitrite degradation was likely dominated by enzymatic activities. Microbial phyla such as Bacteroidetes (38.8%), Proteobacteria (19.2%), and the archaeal phylum Euryarchaeota (1.1%) showed strong correlations with nitrite. Among the genera within these three phyla, Chryseobacterium, Elizabethkingia, and Aeromonas exhibited significant differences in abundance compared to the late fermentation stage and were identified as the primary microbial groups likely driving the enzymatic degradation. During the nitrite degradation period, the nitrite concentration decreased to 0.04 mg/kg, the pH dropped to 3.6, and the abundances of nirK and nirS genes were reduced to 1.0 × 103 copies/μL. At this stage, the nitrite degradation was primarily driven by acid activity. The bacterial phylum Firmicutes (99%) exhibited a strong correlation with pH. Within this phylum, the genus Lactobacillus, which showed significant differences in abundance compared to the early fermentation stage, was identified as the primary microbial group indirectly contributing to acidic degradation. This study provides guidance for the isolation of food-grade prokaryotic microbial strains capable of nitrite degradation. Additionally, the findings offer a methodological reference for conducting future research on nitrite-degrading microorganisms in fermented vegetable broths.

Ochratoxin A Degradation and Stress Response Mechanism of Brevundimonas naejangsanensis ML17 Determined by Transcriptomic Analysis

Ochratoxin A (OTA) is a naturally occurring mycotoxin mainly produced by certain species of Aspergillus and Penicillium and is a serious threat to human health and food safety. Previous studies showed that Brevundimonas naejangsanensis ML17 can completely degrade 1 μg/mL of OTA. The aim of this study was to investigate the degradation effect of ML17 at different concentrations of OTA, and specifically, to investigate the mechanism of OTA degradation by ML17. The growth of ML17 was not affected by exposure to 6 μg/mL OTA within 24 h. ML17 could almost completely degrade 12 μg/mL of OTA within 36 h, converting it into the non-toxic OTα and L-phenylalanine. Transcriptomic analysis showed that 275 genes were upregulated, whereas three genes were downregulated in ML17 under the stress of 1 μg/mL OTA. Functional enrichment analysis showed that exposure to OTA enhanced translation, amide and peptide biosynthesis and metabolism, promoted oxidative phosphorylation, and increased ATP production. Further analysis revealed that, when exposed to OTA, ML17 exerted a stress-protective effect by synthesizing large amounts of heat shock proteins, which contributed to the correct folding of proteins. Notably, genes related to antioxidant activity, such as peroxiredoxin, superoxide dismutase, and glutaredoxin 3, were significantly upregulated, indicating that ML17 can resist the toxic effects of OTA through adjusting its metabolic processes, and the enzyme-coding gene0095, having OTA degradation activity, was found to be upregulated. This suggests that ML17 can achieve OTA degradation by regulating its metabolism, upregulating its antioxidant system, and upregulating enzyme-encoding genes with OTA degradation activity. Our work provides a theoretical reference for clarifying the mechanism of OTA degradation by ML17.

Biodegradation Characteristics and Mechanism of Aflatoxin B1 by Bacillus amyloliquefaciens from Enzymatic and Multiomics Perspectives

Aflatoxin B1 (AFB1), a mycotoxin and natural carcinogen, commonly contaminates cereals and animal feeds, posing serious health risks to human and animal. In this study, Bacillus amyloliquefaciens ZG08 isolated from kimchi could effectively remove 80.93% of AFB1 within 72 h at 37 °C and pH 7.0. Metabolome and transcriptome analysis showed that metabolic processes including glycerophospholipid metabolism and amino acid metabolism were most affected in B. amyloliquefaciens ZG08 exposed to AFB1. The adaptation mechanism likely involved activation of the thioredoxin system to restore intracellular redox equilibrium. The key genes, tpx and gldA, overexpressed in Escherichia coli BL21, achieved degradation rates of 60.15% and 47.16% for 100 μg/kg AFB1 under optimal conditions of 37 °C and pH 8.0 and 45 °C and pH 7.0, respectively. The degradation products, identified as AFD1, were less cytotoxic than AFB1 in HepG2 cells. These findings suggest potential strategies for utilizing probiotics and engineered enzymes in AFB1 detoxification.

Identification of a Novel Aflatoxin B1-Degrading Strain, Bacillus halotolerans DDC-4, and Its Response Mechanisms to Aflatoxin B1

Aflatoxin B1 (AFB1) contamination is a food safety issue threatening human health globally. Biodegradation is an effective method for overcoming this problem, and many microorganisms have been identified as AFB1-degrading strains. However, the response mechanisms of these microbes to AFB1 remain unclear. More degrading enzymes, especially of new types, need to be discovered. In this study, a novel AFB1-degrading strain, DDC-4, was isolated using coumarin as the sole carbon source. This strain was identified as Bacillus halotolerans through physiological, biochemical, and molecular methods. The strain's degradation activity was predominantly attributable to thermostable extracellular proteins (degradation rate remained approximately 80% at 90 °C) and was augmented by Cu2+ (95.45% AFB1 was degraded at 48 h). Alpha/beta hydrolase (arylesterase) was selected as candidate AFB1-degrading enzymes for the first time as a gene encoding this enzyme was highly expressed in the presence of AFB1. Moreover, AFB1 inhibited many genes involved in the nucleotide synthesis of strain DDC-4, which is possibly the partial molecular mechanism of AFB1's toxicity to microorganisms. To survive under this stress, sporulation-related genes were induced in the strain. Altogether, our study identified a novel AFB1-degrading strain and explained its response mechanisms to AFB1, thereby providing new insights for AFB1 biodegradation.

Isolation, identification, degradation mechanism and exploration of active enzymes in the ochratoxin A degrading strain Acinetobacter pittii AP19

Ochratoxin A (OTA) is a polyketide mycotoxin that commonly contaminates agricultural products and causes significant economic losses. In this study, the efficient OTA-degrading strain AP19 was isolated from vineyard soil and was identified as Acinetobacter pittii. Compared with growth in nutrient broth supplemented with OTA (OTA-NB), strain AP19 grew faster in nutrient broth (NB), but the ability of the resulting cell lysates to remove OTA was weaker. After cultivation in NB, the cell lysate of strain AP19 was able to remove 100% of 1 mg/L OTA within 18 h. The cell lysate fraction > 30 kDa degraded 100% of OTA within 12 h, while the fractions < 30 kDa were practically unable to degrade OTA. Further anion exchange chromatography of the > 30 kDa fraction yielded two peaks exhibiting significant OTA degradation activity. The degradation product was identified as OTα. Amino acid metabolism exhibited major transcriptional trends in the response of AP19 to OTA. The dacC gene encoding carboxypeptidase was identified as one of the contributors to OTA degradation. Soil samples inoculated with strain AP19 showed significant OTA degradation. These results provide significant insights into the discovery of novel functions in A. pittii, as well as its potential as an OTA decomposer.

Biotechnological and Biocontrol Approaches for Mitigating Postharvest Diseases Caused by Fungal Pathogens and Their Mycotoxins in Fruits: A Review

Postharvest diseases caused by fungal pathogens are significant contributors to the postharvest losses of fruits. Moreover, some fungal pathogens produce mycotoxins, which further compromise the safety and quality of fruits. In this review, the potential of biotechnological and biocontrol approaches for mitigating postharvest diseases and mycotoxins in fruits is explored. The review begins by discussing the impact of postharvest diseases on fruit quality and postharvest losses. Next, it provides an overview of major postharvest diseases caused by fungal pathogens. Subsequently, it delves into the role of biotechnological approaches in controlling these diseases. The review also explored the application of biocontrol agents, such as antagonistic yeasts, bacteria, and fungi, which can suppress pathogen growth. Furthermore, future trends and challenges in these two approaches are discussed in detail. Overall, this review can provide insights into promising biotechnological and biocontrol strategies for managing postharvest diseases and mycotoxins in fruits.

Transcriptome analysis reveals gene expression changes of the basidiomycetous yeast Apiotrichum mycotoxinivorans in response to ochratoxin A exposure

Ochratoxin A (OTA) is one of the most common and deleterious mycotoxins found in food and feedstuffs worldwide; however, Apiotrichum mycotoxinivorans can detoxify OTA. Our results show that A. mycotoxinivorans GUM1709 efficiently degraded OTA, but it caused the accumulation of intracellular reactive oxygen species. The main aim of this study was to identify potential OTA-detoxifying enzymes and to explore the effects of OTA on A. mycotoxinivorans GMU1709. RNA-seq data revealed that 1643 and 1980 genes were significantly upregulated and downregulated, respectively, after OTA exposure. Functional enrichment analyses indicated that OTA exposure enhanced defense capability, protein transport, endocytosis, and energy metabolism; caused ribosomal stress; suppressed DNA replication and transcription; inhibited cell growth and division; and promoted cell death. The integration of secretome, gene expression, and molecular docking analyses revealed that two carboxypeptidase homologues (members of the metallocarboxypeptidase family) were most likely responsible for the detoxification of both extracellular and intracellular OTA. Superoxide dismutase and catalase were the main genes activated in response to oxidative stress. In addition, analysis of key genes associated with cell division and apoptosis showed that OTA exposure inhibited mitosis and promoted cell death. This study revealed the possible OTA response and detoxification mechanisms in A. mycotoxinivorans.

Unveiling ochratoxin a controlling and biodetoxification molecular mechanisms: Opportunities to secure foodstuffs from OTA contamination

Anarchic growth of ochratoxin A (OTA) producing fungi during crop production, prolonged storage, and processing results in OTA contamination in foodstuffs. OTA in food exacerbates the risk of health and economic problems for consumers and farmers worldwide. Although the toxic effects of OTA on human health have not been well established, comprehensive preventive and remedial measures will be essential to eliminate OTA from foodstuffs. Strict regulations, controlling OTA at pre- or post-harvest stage, and decontamination of OTA have been adopted to prevent human and animal OTA exposure. Biological control of OTA and bio-decontamination are the most promising strategies due to their safety, specificity and nutritional value. This review addresses the current understanding of OTA biodegradation mechanisms and recent developments in OTA control and bio-decontamination strategies. Additionally, this review analyses the strength and weaknesses of different OTA control methods and the contemporary approaches to enhance the efficiency of biocontrol agents. Overall, this review will support the implementation of new strategies to effectively control OTA in food sectors. Further studies on efficacy-related issues, production issues and cost-effectiveness of OTA biocontrol are to be carried out to improve the knowledge, develop improved delivery technologies and safeguard the durability of OTA biocontrol approaches.